Driven by disturbances in the solar wind, geomagnetic storms and substorms energize the near-Earth space environment, causing numerous deleterious effects such as damage to spacecraft materials, communications problems, and spacecraft charging. While hydrogen ions (H+) are ubiquitous in the Earth's magnetosphere, oxygen ions (O+) at keV energies form a substantial but variable component of the Earth's plasma environment. Geostationary Operational Environmental Satellites (GOES) measurements indicate that in the geosynchronous region the concentration of 1–15 keV O+ is highly dependent on geomagnetic activity, local time, and distance from Earth. Additionally, at magnetic shells L˜7–8 (which are defined as the extension of the Earth's dipole magnetic field lines from their radial distance L (in units of earth radii) from the Earth at the Earth's magnetic equator), the most abundant ion during quiet time and moderately disturbed conditions is H+, while during strongly disturbed conditions the O+ density and energy density can be comparable to that of H+ on the dayside magnetosphere.
A summary of results from measurements of the space environment for ions averaged over 0.1–17 keV/e and pitch angles in the range 45°–135° at L˜5 is [W. Lennartsson and R. D. Sharp, “A comparison of 0.1–17 keV/e ion composition in the near equatorial magnetosphere between quiet and disturbed conditions,” J. Geophys. Res. 87 (1982) 6109]:    (1) O+ is typically comparable to H+ in density and is often the dominant species, particularly during quiet times.    (2) The density ratio n(O+)/n(H+) peaks at the lowest magnetic L-shell values and are, on average, higher during quiet times than during the early main phase of major geomagnetic storms.    (3) H+ and O+ have comparable mean energies (usually 2–7 keV) within the measured energy window, and the energies are highest during geomagnetically disturbed times.Not only is O+ a major, but variable, constituent of the terrestrial magnetosphere, O+ can also damage spacecraft materials through a different process than H+. For ion energies less than approximately 50 keV, H+ loses most of its energy (e.g., 94% for 10 keV H+ incident on silicon [H. O. Funsten, S. M. Ritzau, R. W. Harper, J. E. Borovsky, and R. E. Johnson, Energy Loss by keV Ions in Silicon, Phys. Rev. Lett., 92 (2004) 212301–212304.] to excitations and ionizations of electrons in the target material. While this energy loss process cannot damage conductors or semiconductors, in dielectric material this can result in charging (and therefore damaging electrostatic discharges), chemical modification of the material, and degradation of electronics and electrical components. Over the same energy range, O+ loses most of its energy (e.g., 66% for 10 keV O+ incident on silicon [H. O. Funsten, S. M. Ritzau, R. W. Harper, J. E. Borovsky, and R. E. Johnson, Energy Loss by keV Ions in Silicon, Phys. Rev. Lett., 92 (2004) 212301–212304] to Coulombic interactions with nuclei in the target, causing atomic displacement and rearrangement along the ion track in both dielectric and conductive material. This can result in chemical modification, physical modification of the material structure, sputtering, and degradation of electronics and electrical components. Due to the large difference in the types of damage induced by H+ and O+, and substantial variation in abundances of these species, their measurement is critical for understanding the plasma environment and effects on spacecraft materials.
Mass spectrometers have been flown in the Earth's magnetosphere to study the composition of the terrestrial magnetosphere in order to better understand its structure, dynamics, and coupling to the ionosphere and solar wind. These instruments typically utilize a foil-based time-of-flight (TOF) technique in which an ion of known energy transits a thin foil, where it emits secondary electrons that are detected and used to start a timer, and then continues through a drift section and is detected, stopping the timer. The time-of-flight of an ion across a known distance of travel allows the ion's mass to be determined if its energy is known. These TOF instruments, which have a field-free drift section, have a mass resolution m/Δm typically in the range of 7–10. However, these instruments require fast timing circuits, long drift lengths, and, often, multiple detectors, resulting in large mass, volume, and power requirements.
The present invention addresses the negative aspects of prior art instruments by exhibiting simplicity, lower mass, lower power, lower volume, and lower cost, which results from the absence of a traditional drift region that uses considerable volume and the fast timing circuitry of the TOF system.
Various objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims